A molten carbonate fuel cell (MCFC) is a highly efficient and environmental-friendly power generating device. Main constituents of a molten carbonate fuel cell include an anode and a cathode where an electrochemical reaction occurs, a matrix including a carbonate electrolyte, a current collector for electricity collection and gas distribution, and a separator for electrical conduction and gas inflow and outflow, and the like. As the anode current collector, nickel, a nickel alloy, STS 310S or the like stable under an anode environment is used. As the cathode current collector, 316L is used, and as the separator, 316L or 310S is used. The electrolyte is generally present in a molten state at 650° C., an operating temperature of a molten carbonate fuel cell. The current collector and the separator have a problem of facing a risk of corrosion by being exposed to the molten carbonate of 650° C. and gas generated from the anode and the cathode. When corrosion occurs in the current collector and the separator as above, non-conductive corrosion products having high resistance are formed on the stainless steel surface causing an increase in the resistance and an electrolyte loss, which induces a decline in the whole fuel cell performance. Particularly, the STS 316L material currently use as a cathode current collector material of a molten carbonate fuel cell has an advantage of exhibiting excellent electrical conductivity, but has a fatal disadvantage of inducing cell performance decline when used for a long period of time due to a rapid corrosion product increase caused by relatively low corrosion resistance.
As methods of solving a corrosion problem of stainless steel in a molten carbonate fuel cell, methods of applying anti-corrosion coating on a stainless steel surface are disclosed in a method of processing a separator of a molten carbonate-type fuel cell (Korean Patent No. 10-0259213 (2000 Mar. 20)), a coating method of anti-corrosion for a separator of a molten carbonate fuel cell (Korean Patent No. 10-1311784 (2013 Sep. 13)), and a separator for a molten carbonate fuel cell (Korean Patent No. 10-0435420 (2004 Jun. 1)) disclosed in the art.
However, the method of enhancing corrosion resistance by coating nickel or aluminum on a stainless steel surface also has problems although it may facilitate enhancement in the corrosion resistance itself. For example, when forming a nickel coating portion, corrosion resistance may decrease due to a carburizing phenomenon forming carbides on the nickel coating portion, and when forming an aluminum coating portion, aluminum oxide is formed causing a problem of decreasing contact resistance, and the like.
In addition, the method of enhancing corrosion resistance by coating TiN on a part where a separator and an electrode are brought into contact with each other, and coating Ni again thereon may not control conductivity of corrosion products themselves formed on a stainless steel surface, and separator manufacturing costs increase due to additional costs required by the coating.
Accordingly, new stainles steel capable of maintaining high conductivity and corrosion resistance while not including a separate coating process has been required.